CROSS-REFERENCE TO RELATED APPLICATION
This application is related to application Ser. No. 07/439,220 filed on even date, for Solvent Extraction Of Lubricating Oils by A. Sequeira, Jr.
1. Field Of The Invention
The invention relates to solvent refining a petroleum derived lubricating oil stock to yield aromatics lean raffinates. More particularly the invention relates to producing high and medium viscosity index lubricating oils simultaneously.
2. Description Of the Related Arts
It is well known in the art to upgrade lubricating oil stocks. Upgrading typically involves treating these stocks with selective solvents to separate a relatively more aromatic fraction from a relatively more paraffinic fraction. In such a treatment, the preferred configuration comprises a countercurrent extraction process in which the lighter lubricating oil phase is introduced into the center or bottom section of the countercurrent extraction tower. The oil phase flows upwardly through the extraction tower and contacts downwardly flowing solvent which is introduced into the upper section of the extraction tower. A relatively paraffinic fraction, termed raffinate, is recovered from the top section of the extraction tower while solvent and relatively aromatic fraction, termed extract, are recovered from the bottom section of the tower.
Multistage solvent extraction processes are also known wherein either the raffinate phase, the extract phase or both are subjected to repeated extraction to enhance a desired property.
Paraffinic stocks have been upgraded by a combination of solvent extraction followed by hydrogenation in the presence of hydrogenation catalyst at temperatures in the order of 650.degree. F. to 850.degree. F. and relatively high hydrogen partial pressures.
A description of such a process is found in U.S. Pat. No. 3,806,445 to H. C. Henry et al. which describes a process for upgrading a paraffinic fraction to increase viscosity index (VI) and improve ultraviolet (UV) light stability. In the process a lubricating oil stock is solvent extracted to remove aromatics and then catalytically cracked in the presence of hydrogen under mild hydrocracking conditions and then extracted a second time.
U.S. Pat. No. 2,305,038 to F. W. Schumacher describes a process for the solvent extraction of mineral oils. In accordance with the process the oil remaining in the extraction solvent is removed by treatment with a relatively higher boiling oil. The mixture is distilled to effect a separation of extraction solvent as an overhead product and oil as a bottoms product.
U.S. Pat. No. 2,261,799 to J. L. Franklin, Jr. describes a process for the solvent extraction of mineral oils and removal of solvent from raffinates. In accordance with the invention, the extracted oil is reextracted with a secondary solvent which has a preferential selectivity for the primary solvent relative to the mineral oil. A raffinate, reduced in solvent is obtained.
U.S. Pat. No. 2,081,721 to W. J. D. Van Dijck et al. describes improvements in a solvent extraction process.
U.S. Pat. No. 4,328,092 to A. Sequeira, Jr. teaches a process for the solvent extraction of hydrocarbon oils. In the process N-methyl-2-pyrrolidone is the extraction solvent. The hydrocarbon oil is solvent extracted to form two phases, a secondary extract phase and a secondary raffinate phase. The secondary raffinate phase is returned to the extraction zone. As a result, an increased yield of refined oil product and a savings in energy is achieved.
U.S. Pat. No. 4,304,660 to A. Sequeira, Jr. discloses lubricating oils suitable for use as refrigeration oils. Those lubricating oils are produced by solvent extraction of naphthenic lubricating oil base stocks to yield an extract which is mixed with a solvent modifier and cooled to form a secondary raffinate and secondary extract. The secondary raffinate is treated with concentrated sulfuric acid and caustic neutralized to produce the refrigeration oil.